There has been and continues to be a very significant need for effective means of thawing frozen ground. Conventional methods used today are slow and antiquated. For example some may use gas or electric energy to directly heat the ground or use gas or electric energy to heat steam or other mediums, which in turn are applied to the frozen ground. Some processes call for drilling holes deep into the frost and injecting steam or gas flames or even inserting small microwave generators in the drilled holes. The most basic systems utilize heated water or other liquids circulated through grids or hoses on the ground surface to thaw the ground. U.S. Pat. No. 5,838,880 to Brooks, et al., incorporated by reference herein in its entirety, describes such a system. These processes are very slow and use an extreme amount of energy.
Previous microwave ground thawing systems were either low frequency 2.45 MHz or very large 915 MHz units with probes placed in predrilled holes to minimize radiation leakage. Predrilling holes for ground thawing took as much or more time and energy then thawing with gas, steam, or other means. An example of a prior microwave ground thawing system is described in U.S. Pat. No. 4,571,473 to Wyslouzil et al., incorporated by reference herein in its entirety.
There continues to be the need for a more efficient ground thawing system that will quickly heat the ground, but addresses the health risks incumbent with microwave radiation.
U.S. Pat. No. 5,092,706 to Bowen, et al, also incorporated by reference herein in its entirety, discloses a microwave system for repairing voids in asphalt pavement, but utilizes a more mobile system for introducing microwave energy to the ground surface. This system suffers from a lack of control in directing the microwave radiation to the ground. This not only results in inefficiency and increased operating costs, but is also unsafe for workers in the area when the system is operational.
Another system that uses microwaves for road repair is disclosed by U.S. patent application Ser. No. 11/306,979 filed by Hall and incorporated by reference herein in its entirety. This system suffers from the fact that it is a large system and fails to address control of the microwave radiation it generates.
Other methods and systems utilizing microwave technology for asphalt road repair include U.S. Pat. Nos. 4,252,459, 4,252,487, and 4,319,856 to Jeppson and 4,347,016 to Sindelar et al., all of which are incorporated by reference herein in their entirety.